Abstract
In this study, we investigated how the forest composition varies across fine-scale environmental heterogeneity. We established a 25-ha permanent plot, surveyed the micro-topography, and censused all trees with diameter at breast height of ≥ 1 cm within a natural broad-leaved forest in northeastern Taiwan. The micro-topographic differentiation of the forest composition and habitat association of individual species were analyzed using regression tree models and indicator species analysis. Our results demonstrated that nearly 30% of the variation in the tree species composition was attributable to micro-topographic factors in this contiguous forest region. Slope curvature, inclination, and aspect were the decisive factors of micro-topographic niche differentiation. Over 9/10 of the examined species were shown to be indicative of a specific habitat, but each species performed dissimilarly in both the magnitude and breadth of its habitat associations. In addition to niche differentiation, other underlying processes might also be jointly regulating this forest community. In conclusion, our results confirm the control of the niche-assembly rule on tree species diversity and forest structure along micro-topographic gradients in this subtropical rainforest.